The use of enzymes derived from microbial cells to effect specific chemical transformations is well known. In carrying out such transformations, cell-free preparations are commonly employed in batch-type processes. The enzymes are usually liberated from the cell by mechanical means or by autolysis but this is an expensive process which often leads to additional technical problems as well as to questions of economic feasibility. The use of whole cells is also generally avoided because they do not lend themselves to continuous industrial scale processes.
Various difficulties encountered with the use of whole cells as well as cell-free enzymes have led in recent years to an increased interest in the preparation of various forms of immobilized enzymes. Such immobilized enzymes can be used in a batch-wise process as well as in a continuous column process. The use of immobilized enzymes requires separation of the enzyme from the microorganism, purification and attachment to support materials such as dextran or cellulose derivatives, organic resins and glass beads. The processes of extraction, purification and insolubilization are time consuming and are usually accompanied by a substantial loss of initial enzyme activity.
It has long been known that insoluble materials such as cells are more efficiently removed from liquids by the use of polyelectrolytes, natural gums or alum. For example, fermentations involving extracellular enzymes commonly use polyelectrolytes to aid in the removal of the unwanted cells and improve clarity of the enzyme-containing filtrate. Some of the mechanistic aspects associated with the polyelectrolyte flocculation of bacteria are presented by P. L. Busch and W. Stumm in Environmental Science and Technology 2, 49-53 (January, 1968) as well as by L. L. Gasner and D. I. C. Wang in Biotechnology and Bioengineering 12, 873-887 (1970).